We have been studying the efficacy of local injections of botulinum toxin (btx) for the treatment of movement disorders including dystonia, and tremor. When injected in small doses directly into the muscle, botulinum toxin is taken up into the presynaptic neuron at the neuromuscular junction where it prevents the release of acetylcholine. Abnormal muscle contraction is decreased and function improves. Treatment with botulinum toxin is well-tolerated with minimal side effects. We have also been using botulinum toxin to study the physiology of dystonia. We are completing a trial of btx type F for patients with a loss of response to type A due to antibodies. Eighty-five percent had benefit from btx F which was similar to their previous response to type A. One patient with no benefit from type A also had no benefit from type F. A single patient with loss of response but negative antibody testing for type A toxin, had response to type F injection. Over 80% of patients with hand dystonia benefit from botulinum toxin injection. The results of a study on the effects of exercise immediately after botulinum toxin injection are being analyzed to see if exercise enhances btx uptake into active neurons with improvement in the extent or duration of benefit. Eighteen patients with tremor (arm tremor 10, head/neck tremor 8) have been treated to date. Approximately 60% of the tremor patients have more than minimal improvement with btx injection. Data are being collected to assess objectively tremor response to treatment with triaxial accelerometry.